diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/maintainer/maintainer-entry-profile.rst | 1 | ||||
| -rw-r--r-- | Documentation/nvme/feature-and-quirk-policy.rst | 77 | ||||
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 46 | ||||
| -rw-r--r-- | Documentation/virt/kvm/locking.rst | 19 |
4 files changed, 118 insertions, 25 deletions
diff --git a/Documentation/maintainer/maintainer-entry-profile.rst b/Documentation/maintainer/maintainer-entry-profile.rst index 93b2ae6c34a9..cfd37f31077f 100644 --- a/Documentation/maintainer/maintainer-entry-profile.rst +++ b/Documentation/maintainer/maintainer-entry-profile.rst @@ -104,3 +104,4 @@ to do something different in the near future. ../riscv/patch-acceptance ../driver-api/media/maintainer-entry-profile ../driver-api/vfio-pci-device-specific-driver-acceptance + ../nvme/feature-and-quirk-policy diff --git a/Documentation/nvme/feature-and-quirk-policy.rst b/Documentation/nvme/feature-and-quirk-policy.rst new file mode 100644 index 000000000000..c01d836d8e41 --- /dev/null +++ b/Documentation/nvme/feature-and-quirk-policy.rst @@ -0,0 +1,77 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================= +Linux NVMe feature and and quirk policy +======================================= + +This file explains the policy used to decide what is supported by the +Linux NVMe driver and what is not. + + +Introduction +============ + +NVM Express is an open collection of standards and information. + +The Linux NVMe host driver in drivers/nvme/host/ supports devices +implementing the NVM Express (NVMe) family of specifications, which +currently consists of a number of documents: + + - the NVMe Base specification + - various Command Set specifications (e.g. NVM Command Set) + - various Transport specifications (e.g. PCIe, Fibre Channel, RDMA, TCP) + - the NVMe Management Interface specification + +See https://nvmexpress.org/developers/ for the NVMe specifications. + + +Supported features +================== + +NVMe is a large suite of specifications, and contains features that are only +useful or suitable for specific use-cases. It is important to note that Linux +does not aim to implement every feature in the specification. Every additional +feature implemented introduces more code, more maintenance and potentially more +bugs. Hence there is an inherent tradeoff between functionality and +maintainability of the NVMe host driver. + +Any feature implemented in the Linux NVMe host driver must support the +following requirements: + + 1. The feature is specified in a release version of an official NVMe + specification, or in a ratified Technical Proposal (TP) that is + available on NVMe website. Or if it is not directly related to the + on-wire protocol, does not contradict any of the NVMe specifications. + 2. Does not conflict with the Linux architecture, nor the design of the + NVMe host driver. + 3. Has a clear, indisputable value-proposition and a wide consensus across + the community. + +Vendor specific extensions are generally not supported in the NVMe host +driver. + +It is strongly recommended to work with the Linux NVMe and block layer +maintainers and get feedback on specification changes that are intended +to be used by the Linux NVMe host driver in order to avoid conflict at a +later stage. + + +Quirks +====== + +Sometimes implementations of open standards fail to correctly implement parts +of the standards. Linux uses identifier-based quirks to work around such +implementation bugs. The intent of quirks is to deal with widely available +hardware, usually consumer, which Linux users can't use without these quirks. +Typically these implementations are not or only superficially tested with Linux +by the hardware manufacturer. + +The Linux NVMe maintainers decide ad hoc whether to quirk implementations +based on the impact of the problem to Linux users and how it impacts +maintainability of the driver. In general quirks are a last resort, if no +firmware updates or other workarounds are available from the vendor. + +Quirks will not be added to the Linux kernel for hardware that isn't available +on the mass market. Hardware that fails qualification for enterprise Linux +distributions, ChromeOS, Android or other consumers of the Linux kernel +should be fixed before it is shipped instead of relying on Linux quirks. diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 0dd5d8733dd5..deb494f759ed 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5343,9 +5343,9 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO 32 vCPUs in the shared_info page, KVM does not automatically do so and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO be used explicitly even when the vcpu_info for a given vCPU resides at the - "default" location in the shared_info page. This is because KVM is - not aware of the Xen CPU id which is used as the index into the - vcpu_info[] array, so cannot know the correct default location. + "default" location in the shared_info page. This is because KVM may + not be aware of the Xen CPU id which is used as the index into the + vcpu_info[] array, so may know the correct default location. Note that the shared info page may be constantly written to by KVM; it contains the event channel bitmap used to deliver interrupts to @@ -5356,23 +5356,29 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO any vCPU has been running or any event channel interrupts can be routed to the guest. + Setting the gfn to KVM_XEN_INVALID_GFN will disable the shared info + page. + KVM_XEN_ATTR_TYPE_UPCALL_VECTOR Sets the exception vector used to deliver Xen event channel upcalls. This is the HVM-wide vector injected directly by the hypervisor (not through the local APIC), typically configured by a guest via - HVM_PARAM_CALLBACK_IRQ. + HVM_PARAM_CALLBACK_IRQ. This can be disabled again (e.g. for guest + SHUTDOWN_soft_reset) by setting it to zero. KVM_XEN_ATTR_TYPE_EVTCHN This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates support for KVM_XEN_HVM_CONFIG_EVTCHN_SEND features. It configures an outbound port number for interception of EVTCHNOP_send requests - from the guest. A given sending port number may be directed back - to a specified vCPU (by APIC ID) / port / priority on the guest, - or to trigger events on an eventfd. The vCPU and priority can be - changed by setting KVM_XEN_EVTCHN_UPDATE in a subsequent call, - but other fields cannot change for a given sending port. A port - mapping is removed by using KVM_XEN_EVTCHN_DEASSIGN in the flags - field. + from the guest. A given sending port number may be directed back to + a specified vCPU (by APIC ID) / port / priority on the guest, or to + trigger events on an eventfd. The vCPU and priority can be changed + by setting KVM_XEN_EVTCHN_UPDATE in a subsequent call, but but other + fields cannot change for a given sending port. A port mapping is + removed by using KVM_XEN_EVTCHN_DEASSIGN in the flags field. Passing + KVM_XEN_EVTCHN_RESET in the flags field removes all interception of + outbound event channels. The values of the flags field are mutually + exclusive and cannot be combined as a bitmask. KVM_XEN_ATTR_TYPE_XEN_VERSION This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates @@ -5388,7 +5394,7 @@ KVM_XEN_ATTR_TYPE_RUNSTATE_UPDATE_FLAG support for KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG. It enables the XEN_RUNSTATE_UPDATE flag which allows guest vCPUs to safely read other vCPUs' vcpu_runstate_info. Xen guests enable this feature via - the VM_ASST_TYPE_runstate_update_flag of the HYPERVISOR_vm_assist + the VMASST_TYPE_runstate_update_flag of the HYPERVISOR_vm_assist hypercall. 4.127 KVM_XEN_HVM_GET_ATTR @@ -5446,15 +5452,18 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO As with the shared_info page for the VM, the corresponding page may be dirtied at any time if event channel interrupt delivery is enabled, so userspace should always assume that the page is dirty without relying - on dirty logging. + on dirty logging. Setting the gpa to KVM_XEN_INVALID_GPA will disable + the vcpu_info. KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO Sets the guest physical address of an additional pvclock structure for a given vCPU. This is typically used for guest vsyscall support. + Setting the gpa to KVM_XEN_INVALID_GPA will disable the structure. KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADDR Sets the guest physical address of the vcpu_runstate_info for a given vCPU. This is how a Xen guest tracks CPU state such as steal time. + Setting the gpa to KVM_XEN_INVALID_GPA will disable the runstate area. KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_CURRENT Sets the runstate (RUNSTATE_running/_runnable/_blocked/_offline) of @@ -5487,7 +5496,8 @@ KVM_XEN_VCPU_ATTR_TYPE_TIMER This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates support for KVM_XEN_HVM_CONFIG_EVTCHN_SEND features. It sets the event channel port/priority for the VIRQ_TIMER of the vCPU, as well - as allowing a pending timer to be saved/restored. + as allowing a pending timer to be saved/restored. Setting the timer + port to zero disables kernel handling of the singleshot timer. KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates @@ -5495,7 +5505,8 @@ KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR per-vCPU local APIC upcall vector, configured by a Xen guest with the HVMOP_set_evtchn_upcall_vector hypercall. This is typically used by Windows guests, and is distinct from the HVM-wide upcall - vector configured with HVM_PARAM_CALLBACK_IRQ. + vector configured with HVM_PARAM_CALLBACK_IRQ. It is disabled by + setting the vector to zero. 4.129 KVM_XEN_VCPU_GET_ATTR @@ -6577,11 +6588,6 @@ Please note that the kernel is allowed to use the kvm_run structure as the primary storage for certain register types. Therefore, the kernel may use the values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set. -:: - - }; - - 6. Capabilities that can be enabled on vCPUs ============================================ diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index 845a561629f1..a3ca76f9be75 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -16,17 +16,26 @@ The acquisition orders for mutexes are as follows: - kvm->slots_lock is taken outside kvm->irq_lock, though acquiring them together is quite rare. -- Unlike kvm->slots_lock, kvm->slots_arch_lock is released before - synchronize_srcu(&kvm->srcu). Therefore kvm->slots_arch_lock - can be taken inside a kvm->srcu read-side critical section, - while kvm->slots_lock cannot. - - kvm->mn_active_invalidate_count ensures that pairs of invalidate_range_start() and invalidate_range_end() callbacks use the same memslots array. kvm->slots_lock and kvm->slots_arch_lock are taken on the waiting side in install_new_memslots, so MMU notifiers must not take either kvm->slots_lock or kvm->slots_arch_lock. +For SRCU: + +- ``synchronize_srcu(&kvm->srcu)`` is called _inside_ + the kvm->slots_lock critical section, therefore kvm->slots_lock + cannot be taken inside a kvm->srcu read-side critical section. + Instead, kvm->slots_arch_lock is released before the call + to ``synchronize_srcu()`` and _can_ be taken inside a + kvm->srcu read-side critical section. + +- kvm->lock is taken inside kvm->srcu, therefore + ``synchronize_srcu(&kvm->srcu)`` cannot be called inside + a kvm->lock critical section. If you cannot delay the + call until after kvm->lock is released, use ``call_srcu``. + On x86: - vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock |